Creating a custom font size

using fontsize and selectfont (https://en.wikibooks.org/wiki/LaTeX/Fonts):

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[french]{babel}

\begin{document}

Coucou

\fontsize{14pt}{14pt}\selectfont
Coucou

\fontsize{28pt}{28pt}\selectfont
Coucou

\end{document}

I can't figure out how to remove the numbers at the beginning of each line.

Simply remove the line that contains just \@tempa.